1. Field of the Invention
This invention relates to an organic electrolyte cell making use of lithium as anode and of an organic solvent in the electrolyte solution.
2. Description of the Prior Art
An organic electrolyte cell employing as anode active material metal lithium having high electronegativity has been known as one of the cells showing various superior properties such as showing a cell voltage as high as 3 V because of the extremely low electrode potential of metal lithium and a higher energy density of the cell because of the larger electric capacity per unit weight of metal lithium. Accordingly, the application or usage of the organic electrolyte cell has been increased in recent years as a back-up power source for electronic watches or IC memories that demand high reliability for a long period of time.
As shown in FIG. 10, the aforementioned organic electrolyte cell is composed of metal lithium 101 which is an anode active material, cathode pellet 102 formed of cathode active material, a separator 103 impregnated with an organic electrolyte and disposed between the metal lithium 101 and the pellet 102, an anode cup 104 and a cathode cup 105 sealing the overall unit.
The aforementioned organic electrolytic solution may for example consist of an electrolyte such as lithium perchlorate (LiClO.sub.4) or lithium borofluoride (LiBF.sub.4) disolved in a solvent system consisting in turn of one or more of solvents such as propylen carbonate, 1,2-dimethoxyethane, gammabutyrolactone or tetrahydrofuran. The cathode pellet 102 may consist of one or more of carbon fluoride (CF.sub.4), manganese dioxide (MnO.sub.2), copper oxide (CuO), iron disulfide (FeS.sub.2), silver chromate (Ag.sub.2 CrO.sub.4) or titanium disulfide (TiS.sub.2) mixed together with an electro-conduction assistive agent such as graphite or a binder such as tetrafluoroethylene.
It is noted that, in the aforementioned organic electrolyte cell, an important role of the organic electrolytic solution is to provide for satisfactory ionic conduction between the anode or metal lithium 101 and the cathode or cathode pellet 102. It is for this reason that polypropylene non-woven cloth superior in liquid resistance and liquid holding properties is widely used as the separator 103 designed for such ionic conduction as well as electrical separation between the anode and the cathode.
However, the organic electrolyte cell such as described has a drawback that the internal resistance thereof increases with the progress in discharge. This is probably ascribable to the fact that, no matter which of the aforementioned cathode active materials is employed, discharge products are accumulated at the cathode as the discharge proceeds such that, as shown in FIG. 11, the cathode is markedly swollen to compress the separator 103 formed of the non-woven cloth then squeeze out the electrolyte solution held in the separator 103 with resulting obstruction of the ionic conduction between the anode and the cathode. Such increase in the internal resistance impedes effective utilization of the cell such that, when a larger pulse current is produced in the latter or terminal stage of the discharge process, the cell voltage is significantly lowered due to the high internal resistance with the result that, for an application or usage that demands larger pulse current, it is occasionally not possible to make an effective use of the cell capacity.
The separator formed of the non-woven cloth as mentioned hereinabove plays an important role of holding a sufficient amount of the electrolyte solution between the cathode and the anode to provide for good ionic conduction, and another important roll of completely isolating the anode and the cathode to prevent short-circuiting therebetween in the cell. However, it has a drawback that the liquid holding properties are deteriorated owing to the swelling of the cathode as the discharge proceeds.